This invention relates to a method for producing oligosaccharides which are proliferation accelerating factors for bifidobacteria.
In particular, this invention provides a method for producing oligosaccharides for obtaining a sweet saccharide mixture which contains an appropriate balance of monosaccharides useful as sweeteners, and a minimum of unwanted disaccharides, and can provide sweetness and add oligosaccharides to food and drinks with a lower increase in calories than that of conventional additives.
In recent years, it has become evident that the glucose/galactose series oligosaccharides produced from a .beta.-galactosyl transfer reaction of lactose are the main constituents of breast milk oligosaccharides, and act as a proliferation accelerating factor &or bifidobacteria in human intestines (Japanese Patent Publication No 58-20266, etc.).
The oligosaccharides represented by the general formula Gal-(Gal)n-Glc (where Gal is a galactose residue, Glc is a glucose residue and n is an integer from 1 to 4, hereinafter referred to simply as oligosaccharides) have been widely used in a variety of fields, for example, as additives to fermented milk and powdered milk for infants.
A method in which lactose is treated with a .beta.-galactosidase from Aspergillus oryzae (Japanese Patent Publication No. 58-20266) is a typical method for producing oligosaccharides, but the reaction product obtained in the above-described enzyme treatment is saccharide mixture containing disaccharides (mainly unreacted lactose) and monosaccharides (galactose and glucose), in addition to oligosaccharides. The reaction products are ordinarily used as they are, since no method of economically obtaining just oligosaccharides from the mixture has yet been developed, and the sweetness of the monosaccharides can often be advantageously utilized.
Although the above-described conventional production method which uses a .beta.-galactosidase produced by Aspergillus oryzae provides a high yield of oligosaccharides in a shorter time than that when the .beta.-galactosidase is produced by other microorganisms, this method has a disadvantage in that it remains large quantities of disaccharides, mainly unreacted lactose. These disaccharides have almost no sweetness and so can not be used as a source of sweetness, and from the aspect of lactose intolerance, it is desirable to have as little lactose as possible in the final product.
A reaction product having a lower amount of disaccharides can be obtained from a .beta.-galactosidase with a longer treatment time, but a noticiable reduction in the yield of oligosaccharides cannot be avoided in such a case.
Therefore, when heretofore conventional oligosaccharides are to be added to food and drink, a product which has high oligosaccharide content and thus contains a great deal of disaccharides but a relatively small amount of monosaccharides is commonly used. Further, a sweetener such as sucrose cane sugar) or liquid sugar is also added if the food or drink needs more sweetness, so the resultant food or drink is high in calories because of its exceedingly high saccharide content.
The purpose of the present invention is to solve the above-described problems in the utilization of oligosaccharides.